1. Field of the Invention
This invention relates to a semiconductor process, and in particular, to a method for clearing native oxide.
2. Description of the Prior Art
Along with rapid progress of semiconductor technology, the dimensions of semiconductor devices are reduced and the integrity thereof promoted continuously to further advance the operating speed and performance of the integrated circuit. As the demand for device integrity is raised, the changes in physical properties, such as contact resistance between the devices, have to be considered to avoid a great impact on the operating speed and performance of the circuit.
Taking the formation of a contact plug as an example, after a contact hole is formed but before the contact hole is filled with conductive material, a clearing process is generally conducted to clear the impurities or native oxide at the bottom of the contact hole so as to reduce the contact resistance. Nevertheless, there are still some problems in the foregoing method, so that the performance of the circuit is reduced.
FIGS. 1A-1B are schematic cross-sectional views illustrating a conventional fabrication process of a contact plug. As shown in FIG. 1A, a dielectric layer 102 has been formed on a silicon substrate 100, and a contact hole 104 has been formed in the dielectric layer 102 exposing a partial surface of the silicon substrate 100. As the exposed surface of the silicon substrate 100 contacts with the atmosphere, an oxidation takes place so that a native oxide layer 106 is formed at the bottom of the contact hole 104. A conventional method removes the native oxide layer 106 in a physical manner with argon (Ar) sputtering to solve the problems arising form the native oxide layer 106. However, the removal performance of the native oxide layer 106 by means of Ar sputtering is not satisfactory due to the high aspect ratio of the contact hole 104 formed in current fabrication processes.
As shown in FIG. 1B, a facet 110 is formed at the sidewall of the contact hole 104 during the Ar sputtering because of the arrival angle of Ar ion. While the contact hole 104 is filled with a conductive layer 108 in the later process to accomplish the contact plug, the conductive layer 108 formed between adjacent contact holes 104 tends to bring a bridging 112 due to the facet 110. Accordingly, the electrical properties of the devices are subjected to serious impact. Moreover, as the dimensions of the devices are miniaturized, by-products produced from the sputtering process are easily re-deposited in the contact hole 104, so that the profiles and critical dimensions of the contact hole 104 are changed.
As a result, how to effectively clear native oxide and also ensure the quality of the later-formed devices to improve the process reliability and device performance is one of the immediate issues to be solved in the art.